The present invention relates to a brake lining arrangement with wear indicator, comprising a planar lining carrier with a brake lining attached to a substantially plane holding surface, wherein the wear indicator has a supporting section, with which it is supported on the lining carrier, and an indicator section which extends beyond the holding surface in such a manner that it overlaps the material thickness of the brake lining and indicates a lining wear limit value, wherein the indicator section and supporting section are connected to each other via a transition section, wherein the transition section has a transition section axis.
Such brake lining arrangements are generally known from the prior art and are used in particular in brake systems of motor vehicles. To obtain a braking action in these arrangements, a frictional contact is made between an outwardly facing contact surface of the brake lining and a component of the vehicle to be braked, such as, for example, a brake disc rotating jointly with a wheel. The brake lining arrangement is moved, in a manner known per se, from a rest position free of frictional contact into a braking-active position under external force action and pressed with varying strength against the component to be braked.
The brake lining at first has an initial material thickness with which it extends transversely to the holding surface of the lining carrier. With increasing operating time of the brake lining arrangement, the material thickness decreases progressively as a result of wear phenomena during the frictional contact. After reaching a certain amount of wear, however, reliable functioning of the brake lining arrangement can no longer be ensured. In particular, the risk increases of the material thickness of the brake lining being reduced to such an extent that the lining carrier comes into direct contact with the component to be braked, whereby the respective components may be damaged.
It is therefore generally necessary to replace the brake lining arrangement or renew the brake lining on the lining carrier at the latest when a maximum lining wear limit value, i.e. a maximum permissible reduction of the material thickness of the brake lining, is reached. This presupposes that the reaching of the lining wear limit value or a proximity to this can be detected by a driver of the motor vehicle or a maintenance mechanic.
In order to obtain feedback on the state of wear of the brake lining, wear indicators of the kind described at the outset are used in the prior art. The documents WO 2013/011490 A1, U.S. Pat. No. 5,033,590, EP 0 596 761 A1, DE 295 14 892 U1, DE 10 2011 087 140 A1, DE 41 10 867 A1, U.S. Pat. No. 5,299,663 A, U.S. Pat. No. 4,085,824 A and JP S64-79 435 A disclose typical examples on this. In these, the wear indicators extend with a substantially plane indicator section beyond the holding surface of the respective lining carriers in such a manner they project into a cross-sectional plane of the brake lining or overlap the material thickness of the brake lining by the amount of the lining wear limit value. This means that the indicator section initially provides visual feedback on the state of wear of the brake lining, since the distance between the contact surface of the brake lining and the overlapping end of the indicator section can be detected by inspection. A maintenance mechanic can thus detect by checking this distance the likelihood of the lining wear limit value soon being reached and assess the need to replace the brake lining arrangement or renew the brake lining.
If, however, the lining wear limit value is reached or exceeded during the operation of the brake system, the indicator section comes into direct contact with the component to be braked. Due to the resulting frictional contact, noises are generated which are perceptible, for example, by a driver of a vehicle, so that the driver recognises the need to check the brake system. However, this presupposes that the wear indicator is designed to compensate for the high action of transverse forces during the frictional contact and maintain the frictional contact over a longer operating time and greater number of braking procedures. If, for example, the indicator section breaks off after only a few braking procedures or is plastically deformed in such a manner that it can no longer establish a frictional contact with the component to be braked, the merely temporarily achieved noise effect may possibly not be sufficient to draw the driver's attention sufficiently to the fact that the brake wear limit value has been reached.
It is therefore generally necessary to design the wear indicator in such a manner that the stresses generated therein during a frictional contact are kept low, so that the forces acting are compensated for purely elastically and a high fatigue strength is ensured. Such properties are combined below for simplification under the term “strength” of the wear indicator.
To achieve sufficient strength, customarily a one-piece metal strip is bent a plurality of times in order to produce the sequence of indicator section, transition section and supporting section mentioned at the outset. The indicator section is in this case of substantially plane form and extends at right angles to the holding surface from one side of the lining carrier, on which it overlaps the material thickness of the brake lining, to the side of the lining carrier facing away from the brake lining. There it is connected by a transition section to the likewise plane supporting section or merges into the latter. Starting from the transition section, the supporting section customarily runs firstly parallel to the indicator section and has additionally an angled-away fastening section, with which the wear indicator is fastened in a known manner to the holding carrier. The transition section thus connects the supporting and indicator sections which firstly extend parallel, and in doing so customarily spans an angle of approx. 180°. The transition section is bent around an axis called the transition section axis below, which extends substantially transversely through the transition section and runs, according to the prior art, parallel to the holding surface.
Such a solution is also known from the document U.S. Pat. No. 6,691,835 B 1. In this case, the wear indicator is formed as a one-piece metal bent part which is attached via a supporting section to a rear side of a brake lining carrier facing away from the brake lining. Furthermore, there is provided an indicator section in the form of a rectangular arm which extends to the front side of the brake lining carrier and overlaps the brake lining. For this purpose, the indicator section is angled with respect to the supporting section, the angled region constituting a transition section of the wear indicator. The transition section axis accordingly again runs parallel to the holding surface or in the plane of the brake lining carrier. Additionally, the indicator section in this solution is spirally twisted about it longitudinal axis.
When a frictional contact is produced between wear indicator and component to be braked, in particular the transition section is subjected to high loads. This section connects the indicator section, forming a free end of the wear indicator, and the supporting section supported on the lining carrier or directly fastened thereto. Under corresponding force action in the indicator section, the latter is deflected in a swinging manner relative to the supporting section, resulting in high bending stresses in the transition section. Accordingly, the transition section is a particularly critical region for the strength of the wear indicator. It has turned out, however, that the strength is insufficient in the solutions known from the prior art and safe functioning of the wear indicator in the sense of a sufficiently reliable and lasting noise generation is not ensured.